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    <title>Document</title>
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    <script>
        /* 
        indexOf()
        slice()
        includes()  --判断数组是否包含某个值 */
        var arr=['html','css','javascript']
        var app=[1,2,3,4,5,6,7]
        console.log(arr.indexOf('css'))
        console.log(app.slice(0,4))
        console.log(arr.includes("1"))
    </script>
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